Nikon has the clear edge right now in terms of AF, FPS, and high ISO performance in the $2,500-and-up segment. Like you, I've considered making the switch recently, but decided that since I've toughed it out this long, I might as well wait a few more months until Canon makes some major announcements and reveals its strategy for the 1D and perhaps the 5D series bodies.
Your needs may differ, but a huge consideration is how much comparable Nikon glass would cost compared to the Canon gear you have now. My primary lenses are the 17-40L, 24-105L, and the 70-300L. In pricing out what it would cost to cover a similar range of focal lengths with Nikon glass, Canon lenses seemed like a much better value. Then there's all the little BS that needs replacement which will add up quickly, like flashes, cable releases, filters, wireless triggers, etc.
To put it succinctly, for my shooting needs - where I'm willing to sacrifice megapixels for superior AF, ISO, and FPS - I think Nikon has superior bodies at the moment. However, I still think Canon has a better overall system, and the momentum will shift once again after Canon updates its bodies.